A known camera as an imaging system constituted by a photographing optical system and an imager has a focus adjusting function to enable the tracking of a moving body in accordance with contrast AF to adjust the focus by searching for a position corresponding to the greatest contrast while moving a focus lens on the basis of an image obtained by the imager.
Patent document 1 (Japanese Laid-open Patent Publication No. 2010-015131) discloses a focus adjusting apparatus that uses a contrast AF scheme wherein a focus is adjusted by tracing a moving body. According to a method disclosed in patent document 1, before a main exposure is started, both a diaphragm and a focus lens are simultaneously driven under predictive auto-focusing on moving subject, thereby adjusting the focus in conformity with the main exposure. Patent document 1 also discloses driving a focus lens after performing a main exposure, in preparation for a scan driving operation in a next AF operation.